This invention relates generally to methods for manufacturing pet foods and, more particularly, to manufacturing high protein and fat content dry pet foods.
Pet foods are generally formulated for complete and balanced nutrition of animals. Typically, relative proportions of carbohydrates (such as starch), proteins, and fats in the food ingredients are blended together according to a desired formula, and the blend is moistened and extruded to a desired shape and size. During the extrusion process, the blend is subjected to high temperature, pressure, and shear that results in a continuous plastic melt of polymers which binds together particulate matter as the melt travels down an extruder barrel. When the melt exits an extruder die, the melt is suddenly exposed to atmospheric pressure, and gases formed in the melt are released, thus enabling a porous expanded structure to be formed. The expanded material is cut into smaller pieces and dried to a final moisture content. The cut pieces are coated with fat and palatability enhancers to complete the pet food product.
In the extrusion process, the relative proportions of carbohydrate and protein in a given pet food formulation determine the characteristics of the continuous melt and the binding of materials therein as the food is manufactured, thereby determining the strength and hardness of the extrudate in the manufacturing process. Fats and oils lubricate the compressed polymer mix and modify end product properties and eating qualities of the extruded products. For certain proportions of carbohydrates and protein in a pet food formulation, conventional extrusion processes have proven satisfactory to manufacture dry pet foods.
Recent advances in pet nutrition, however, have made pet food formulas with increased proportions of protein and fat desirable in both special needs diets as well as in starter diets for young pets. High protein and fat pet foods, however, are problematic from a manufacturing perspective. With respect to known extrusion processes, high protein and fat formulas, and the resultant lower carbohydrate content, adversely affect the extrudate so that it will not hold together as it exits the extruder. Solid formation of the pet food product is difficult, and a friable extruded product is produced that is subject to excessive breakage during subsequent processing and handling of the product.